Over 120 mutations in the gene encoding SOD1 are associated with amyotrophic lateral sclerosis. SOD1 mutations result in a toxic property, and a prevailing hypothesis is that a gain-of-function involves dissociation of the SOD1 dimer followed by aggregation. As a result, stabilization of the SOD1 dimer has become an approach for SOD1 therapy. We have discovered a specific and stoichiometric method for stabilizing the SOD1 dimer by tethering Cys111 residues with a covalent cross-linker. Cys111 is a surface residue situated at the dimer interface, and only a short distance apart from the Cys111 (8[unreadable]) on an opposing monomer. Our hypothesis is that compounds that bridge Cys111 residues will function as novel pharmacological chaperones that stabilize fALS SOD1 variants and that peptide-based cross-linkers are suitable for developing a quantitative structure activity model that can be used to create a second generation of improved peptides. In the hopes of inspiring interest, our first aim is to expand the scope of our original findings to include the five most prevalent fALS variants. While our first generation cross-linkers work well in vitro, they known to be toxic in vivo. Therefore, our second aim is to create a new class of peptide-based chemicals that are optimized to cross-link Cys111. PUBLIC HEALTH RELEVANCE: The neurodegenerative diseases, including ALS, have proven extraordinarily difficult to treat, for example, ALS has only one FDA-approved drug for its treatment, reporting little or no effect on patient survival and quality of life. Until recently researchers did not understand the mechanism of ALS- associated proteins'toxicity, but now many believe this involves the dissociation of the protein SOD1 from a dimer into two monomers. Preventing this dissociation has become a focus for therapy, and we have discovered a novel and effective in vitro strategy for stabilizing SOD1 that cross-links individual monomers. This proposal aims to expand the scope of our original findings by testing the most prevalent SOD1 variants, and to develop and optimize molecules that are less toxic than our first generation of cross-linkers.